1. Field of the Invention
The invention relates to a radial, active magnetic bearing apparatus comprising at least three electromagnets that are distributedly arranged in the bearing wherein a rotary current controller is provided for the excitation of the coils of the electromagnets.
2. Description of the Prior Art
A radial, active magnetic bearing for the contact-free journalling of a rotatable body is known from EP 0 612 928. A magnetic bearing of this kind comprises in each case three electromagnets respectively mutually displaced by 120xc2x0 in the circumferential direction, with each of the three electromagnets being supplied with electrical energy by a separate amplifier. A disadvantage of this known magnetic bearing is to be seen in the fact that three separate power amplifiers are required, which are in addition specifically matched and are therefore relatively expensive.
The object of the present invention is to provide an economically more advantageous, active magnetic bearing apparatus.
A radial, active magnetic bearing uses the so-called Maxwell force in order to maintain a rotating part in suspension without contact. This Maxwell force is the reason for the force of attraction of magnetically conducting bodies which are located in a magnetic field.
The object of proposing an economically more advantageous radial, active magnetic bearing based on the Maxwell force is satisfied, in particular, wherein at least three electromagnets are distributedly arranged in the bearing; and wherein a rotary current controller is provided for the excitation of the coils of the electromagnets.
An advantage of the invention is to be seen in the fact that a conventional, three-phase rotary current controller or a three-phase converter can be used as a rotary current controller. These rotary current controllers are a standard product for the excitation of electrical machines. For this reason, a rotary current controller of this kind can be obtained at a very favorable cost.
A further advantage is to be seen in the fact that a conventional three-phase rotary current controller usually has an integrated micro-controller which can be used for control tasks. To use the rotary current controller as an excitation device for an active magnetic bearing, a correspondingly adapted control procedure is required which usually can be stored in the micro-controller of the rotary current controller in the form of program lines (software). Thus, the signal processing, which is complicated and expensive per se, can largely be carried out by the micro-controller integrated into the rotary current controller, which saves on the costs for an additional signal processing apparatus.
The active magnetic bearing in accordance with the invention can be designed as an inner rotor, i.e. with a rotor disposed inwardly, or as an outer rotor, i.e. with a rotor surrounding the electromagnets outwardly. The active magnetic bearing requires a bias magnetization which can be produced by a permanent magnet or by a coil with a direct current component.